1. Field of the Invention
The present invention relates generally to safety devices for powered equipment, and more specifically to a safety retainer for installing at the output end of a power take off (PTO) shaft. The present safety guard or retainer secures to the article of equipment which is being powered by the PTO shaft, and serves to retain that end of the PTO shaft in the event of U-joint breakage or other problem leading to the accidental disconnection of the rotating PTO shaft(from the equipment being driven or powered.
2. Description of the Related Art
The modern farm utilizes a great number of auxiliary powered devices, ranging from grain augers and vacuums to livestock feed grinders and mixers and various other devices. In addition, there is a great deal of portable, or semi-portable, farm or other equipment which is powered by a remotely located powerplant. (combustion engine, electric motor, etc.) with a relatively long shaft extending from the powerplant to the driven equipment (carnival and amusement park rides, saw mills, generators, etc.).
In the case of farm equipment, a single powerplant may be used to power such equipment, with the operator moving the powerplant to the desired article of equipment requiring power for any given operation. In fact, such a procedure is nearly universally used today, with the portable powerplant comprising a tractor with a selectively engageable power take off (PTO) drive off the rear differential. The procedure used is to position the tractor near the machinery to be driven, connect the power take off shaft to the power take off output of the tractor and to the article of equipment to be powered, and engage the power take off drive of the tractor. Other equipment (portable circus and carnival rides, portable sawmills, etc.) are operated in much the same manner, with the exception that the power source may not be capable of moving under its own power, but may have to be positioned by another vehicle.
An important consideration of such equipment, is the rotation of the power take off shaft when the machinery is in operation. Accordingly, various guards have been developed in the past, as will be seen in the discussion of the related art further below. Also, on rare occasions the power take off shaft will separate from either the driven end (i.e., the end at the power source) or the output end (i.e., the end at the equipment being driven), due to breakage of a U-joint, loss or breakage of a connector pin, or even a possible gearbox failure, which would allow the shaft to slip from the gearbox.
Accordingly, tractors are almost universally equipped with PTO output safety guards of some sort, generally comprising a three sided box, enclosing the PTO output area of the tractor on the top and both sides. This is beneficial in providing protection to the tractor operator, but does nothing for safety at the opposite end of the PTO shaft. It will be seen that when the PTO shaft disengages at the driven end, that it will eventually come to rest due to the removal of power from the machine linkage (with mechanical inertia perhaps continuing to cause machinery movement for some period of time.)
However, disconnection of the PTO shaft at the output end, distal from the powerplant, allows the PTO shaft to continue to whip around under power from the power source (tractor, stationary powerplant, etc.). Such shafts are relatively massive, weighing perhaps fifty pounds or more depending upon their length and diameter, in order to transmit the perhaps several hundred pound-feet of torque which may be developed by the powerplant. Not only does this pose a great potential hazard, but it can be most difficult, if not impossible, for an operator to reach the powerplant to shut down operation under the circumstances. Indeed, the present inventor is aware of at least one fatal accident which occurred to a close friend under the circumstances described, when the output end of a PTO shaft separated from the device being driven and whipped violently, striking the operator.
Yet, very little development has occurred in guards or retainers for the output end of a PTO shaft, distal from the driven end at the powerplant. This is perhaps due to the wide variety of equipment which is powered by such mechanisms, and the difficulty in providing a universal guard or shaft retainer for such devices. Accordingly, a need will be seen for power take off (PTO) shaft safety guard or retainer which is removably or permanently installable on a variety of different equipment, adjacent the PTO shaft input to that equipment. The guard or retainer must serve to retain the output end of the PTO shaft opposite its powered end, i.e., the end attached to the powerplant or drive system, to retail the output end of the shaft in the event of mechanical breakage or accidental disconnection of the shaft from the device being driven by the shaft, when the equipment is being operated and the shaft is turning. A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.
U.S. Pat. No. 1,478,953 issued on Dec. 25, 1923 to Leonard Happ et al., titled "Guard," describes a conical screen for guarding the flyweights of an open speed governor mechanism. A stationary rod affixed to an overhead structure passes through the apex of the cone, with the cone being adjustably positionable on the rod. The stationary rod precludes passage of a PTO shaft through the cone, with the result being that the Happ et al. device cannot be used to preclude lateral movement of a rotary PTO shaft passing therethrough, as provided by the present invention.
U.S. Pat. No. 3,389,763 issued on Jun. 25, 1968 to Harold W. Meinert, titled "Guard For Tractor Power Takeoff Shaft," describes a generally three sided guard with an open bottom, unlike the completely surrounding guard of the present invention. The Meinert guard is adapted for quickly removable attachment to the differential of a tractor, for ease of access to the PTO coupling mechanism. While the Meinert guard serves to protect the tractor operator from an upwardly projected powered or input end of a PTO shaft in the event that it accidentally becomes separated from the PTO output of the tractor for any reason while in operation, it does nothing to protect an operator at the output end of the PTO shaft when the assembly is being used to drive a stationary device of some sort.
U.S. Pat. No. 4,308,931 issued on Jan. 5, 1982 to Jagdish C. Khanna, titled "Guard For Drive Shaft In An Articulated Tractor," describes two independent guards, each of which partially surround the driveshaft of the articulated tractor. Each is affixed to a stationary component at each end of the driveshaft, and are configured to overlap without contact when the tractor is turned to produce an angle in the driveshaft. Each shield or guard covers only the top, left, and right sides of the driveshaft, with the bottom of the driveshaft being left unguarded, while the present guard or retainer surrounds the entire shaft near the output end thereof.
U.S. Pat. No. 4,432,742 issued on Feb. 21, 1984 to Wayne E. Hartman, titled "PTO Master Shield," describes a guard or shield covering the top, left, and right sides of a PTO output shaft, and somewhat resembling the guard of the Meinert '763 U.S. Patent discussed further above. Hartman provides an automatic release which rests upon the stationary PTO shaft, and drops the guard into position when the PTO shaft is rotated. However, the bottom of the guard is open, leaving the shaft unguarded in that direction, unlike the completely surrounding guard of the present invention. Moreover, the Hartman guard is hingedly secured directly to the same structure as the PTO shaft, while the present surrounding guard is supported by a strut extending from the mechanism receiving the PTO shaft, with clearance being defined between the encircling PTO shaft retainer and the structure to which the PTO shaft is connected.
U.S. Pat. No. 4,553,950 issued on Nov. 19, 1985 to Christian M. Teich, titled "Flip-Up Shield Assembly For Tractor Power Take-Off," describes a three sided shield having a slotted hinge arrangement. The shield may be adjustably positioned about the hinge pins by means of the slots, to provide clearance for larger U-joint guards on various PTO shafts when they are coupled to the PTO output. The hinged configuration requires that the bottom be left open for clearance in the raised position, unlike the completely surrounding retainer or guard of the present invention. Moreover, the device is secured directly to the PTO structure with no clearance therebetween, unlike the present invention.
U.S. Pat. No. 4,568,313 issued on Feb. 4, 1986 to Harold R. Diffenderfer et al., titled "Protective Guard For Articulated Shafting," describes a telescoping tube with a flexible bellows at each end thereof, for completely enclosing a PTO shaft and U-joints at each end thereof. The Diffenderfer et al. device is not connected to any other structure, and so rotates with the PTO shaft unless some other retaining means is provided, such as the non-rigid chain mentioned by Diffenderfer et al. In contrast, the present guard or retainer completely encircles the PTO shaft only at one point near its output attachment end, with the guard being rigidly connected to the fixed structure of the machinery being driven by the PTO shaft and defining a clearance therebetween.
U.S. Pat. No. 4,663,984 issued on May 12, 1987 to William Taylor, titled "Safety Guard For Power-Take-Off Shaft," describes an articulated bellows completely surrounding the entire shaft, including the U-joint couplings at each end thereof. Specialized housings are provided at the output and input respectively of the machinery powering and being powered by the PTO shaft, for specially configured flanges to secure thereto. A secondary, inner guard is provided surrounding the PTO shaft and inside the bellows, to preclude contact between the PTO shaft and the relatively stationary bellows. The Taylor device does not provide a rigid guard or retainer surrounding only a portion of the shaft and providing clearance between the retainer and the machinery being powered by the PTO shaft, as is accomplished by the present invention.
U.S. Pat. No. 4,761,152 issued on Aug. 2, 1988 to Gerald L. Wagenbach, Jr., titled "Foldable Power Take-Off Shaft Shield," describes a PTO guard secured directly to the PTO structure of a tractor. The device comprises two fixed side plates with a movable upper plate which is selectively positionable between a lowered and a raised state, depending upon the linkage between the upper plate and the side plates. The entire lower area of the device is open, unlike the completely surrounding guard or retainer of the present invention.
Finally, U.S. Pat. No. 5,674,129 issued on Oct. 7, 1997 to Stephen E. Burns et al., titled "Adjustable Shield For Power Take-Of f Shaft," describes a shield having the same basic structure as that described immediately above in the Wagenbach, Jr. '152 U.S. Patent. The device has two immovably affixed side plates and a movable top plate, with the bottom of the guard structure remaining open, unlike the completely encircling retainer or guard of the present invention. The Burns et al. shield utilizes a different slot configuration than Wagenbach, Jr. for adjusting the position of the movable upper plate relative to the fixed side plates, but otherwise the distinctions between the Wagenbach, Jr. device and the present invention are also felt to apply here.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.